UV-bandpass filter and application to UV-detecting apparatus or light-emitting apparatus

ABSTRACT

A UV-bandpass filter for transmitting therethrough light having a wavelength included in a UV-region. The bandpass filter is an optical filter including a thin silver film; wherein the thin silver film includes an entrance face and an exit face opposing the entrance face, for emitting light having a wavelength included in a specific UV-region whose wavelength ranges from 250 nm to 400 nm in the light having reached the entrance face, and has such a thickness as to yield a transmittance of 10% or less with respect to light having a wavelength excluding the specific UV-region.

TECHNICAL FIELD

The present invention relates to a UV-bandpass filter which selectivelytransmits therethrough light having a wavelength included in aUV-region, a UV-detecting apparatus including the same, and a UV source(light-emitting apparatus) including the same.

BACKGROUND ART

Conventionally known as an optical filter having a transmissioncharacteristic with respect to light in a UV-region is, for example, onemade by SCHOTT Corporation (catalog number: 3555eIX/84) havingtransmission characteristics such as those shown in FIG. 1. While FIG. 1shows transmission characteristics of four kinds of optical filters,each tends to exhibit transmission peaks in both UV- and IR-regions.

On the other hand, silver films have been known to exhibit excellentspectral reflection characteristics with respect to light excluding theUV-region. Known as an optical filter utilizing such a silver film is,for example, one using a silver film as a reflecting mirror disclosed inJapanese Patent Application Laid-Open No. SHO 60-252303. This opticalfilter comprises such a structure that the silver film absorbs light inthe UV-region but reflects light in the other wavelength regions,whereas light in the IR-region from the reflected light is blocked byuse of a prism, so as to detect visible light.

DISCLOSURE OF THE INVENTION

The inventors studied conventional optical filters and, as a result,have found the following problems. Namely, while optical filters havingtransmission characteristics such as those shown in FIG. 1 surelyexhibit an excellent transmission characteristic with respect to lightin the UV-region, they also exhibit a transmission characteristic withrespect to light in the IR-region near a wavelength of 700 nm. When anoptical filter having such transmission characteristics is utilized inan inexpensive light-receiving device mainly made of silicon, forexample, having a light-receiving sensitivity up to near 1000 nm so asto be employed in a UV-detecting apparatus for detecting light includedin the UV-region, UV-rays are hard to detect due to the transmission oflight in the IR-region.

Though the optical filter disclosed in Japanese Patent ApplicationLaid-Open No. SHO 60-252303 utilizes a silver film as a reflectingmirror, it merely eliminates light in the UV-region by absorption, andis hard to apply to UV-detecting apparatus for detecting light in theUV-region.

The inventors have found that a single silver layer having an excellenttransmission characteristic with respect to only light in a specificwavelength region included in the UV-region in a wide wavelength bandranging at least from 200 nm to 3000 nm can be obtained whentransmission characteristics of a thin silver film is appropriatelyregulated by controlling its thickness, thereby achieving the presentinvention, whose object is to provide a UV-bandpass filter comprising astructure having an excellent wavelength selectivity with a simpleconfiguration while enabling wide applications, a UV-detecting apparatusincluding the same, and a UV source (light-emitting apparatus) includingthe same.

The UV-bandpass filter according to the present invention is an opticalfilter for selectively transmitting therethrough light having awavelength included in a specific UV-region having a wavelength rangingfrom 200 nm to 400 nm, preferably a wavelength ranging from 250 nm to400 nm, more preferably a wavelength ranging from 300 nm to 360 nm,while absorbing or reflecting light having a wavelength excluding thespecific UV-region, wherein the UV-bandpass filter includes a thinsilver film comprising an entrance face and an exit face opposing theentrance face, for emitting the light having a wavelength included inthe specific UV-region in the light having reached the entrance face,and reduces the ratio of light excluding the UV-region to 10% or less inthe transmitted light emitted from the exit face.

In particular, the thin silver film has such a thickness as to exhibit atransmittance of 10% or less, preferably 5% or less, with respect tolight having a wavelength excluding the specific UV-region. Namely, theinventors have found it necessary to suppress the transmittance forlight having a wavelength of 400 nm or more to a value of 10% or less,preferably 5% or less, in order to make it possible to detect UV-rays,which necessitates a film thickness of 70 nm or more, preferably 80 nmor more. On the other hand, the inventors have found that a filmthickness of 250 nm or less is required since it is necessary to securea transmittance of 5% or more with respect to light in theabove-mentioned specific UV-region in view of the light-receivingsensitivity of UV detectors.

Further, the UV-bandpass filter according to the present invention maybe constituted by a member transparent to at least UV-rays(UV-transmitting member) prepared as a reinforcement member, and a thinsilver film formed on a surface of the UV-transmitting member. When theUV-bandpass filter and a light-receiving device are combined together,aUV-detecting apparatus is obtained. In this case, the thin silver filmis directly or indirectly formed on a light entrance face of thelight-receiving device. For example, when the light-receiving device hasan entrance faceplate, the thin silver film may be formed on theentrance faceplate as well (whereby the entrance faceplate functions asa reinforcement member for the thin silver film).

Furthermore, when the UV-bandpass filter and a light-emitting device arecombined together, a UV source (light-emitting apparatus) is obtained.In this case, the thin silver film is directly or indirectly formed on alight exit face of the UV source. For example, when the light-emittingdevice comprises an envelope which transmits light therethrough, thethin silver film maybe formed on a surface of the envelope (whereby theenvelope itself functions as a reinforcement member for the thin silverfilm).

Embodiments according to the present invention will become more fullyunderstood from the detailed description given hereinbelow and theaccompanying drawings. These embodiments are given by way ofillustration only, and thus should not be considered limitative of thepresent invention.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, it isclear that the detailed description and specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only, and various changes and modifications within thespirit and scope of the invention will become apparent to those skilledin the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing transmission characteristics of typicalUV-bandpass filters;

FIGS. 2A to 2C are views showing respective structures of first to thirdembodiments of the UV-bandpass filter according to the presentinvention;

FIG. 3 is a graph showing respective wavelength dependencecharacteristics of transmittance in five kinds of thin silver filmshaving thicknesses (12.8 nm to 78.4 nm) different from each other;

FIG. 4 is a graph showing respective wavelength dependencecharacteristics of transmittance in the five kinds of thin silver filmsshown in FIG. 3 when their maximum transmittances are taken as 100%;

FIG. 5 is a graph showing respective wavelength dependencecharacteristics of transmittance in six kinds of thin silver filmshaving thicknesses (80.4 nm to 400.0 nm) different from each other;

FIG. 6 is a graph showing respective wavelength dependencecharacteristics of transmittance in the six kinds of thin silver filmsshown in FIG. 5 when their maximum transmittances are taken as 100%;

FIG. 7 is a graph showing respective relationships between the thicknessof a thin silver film and its transmittance with respect to light havinga wavelength of 322 nm (transmission peak wavelength);

FIG. 8 is a graph showing respective relationships between the thicknessof a thin silver film and the relative transmittance with respect to aplurality of wavelengths (400 nm, 500 nm, and 600 nm) of light withreference to the maximum transmittance at a transmission peak wavelengthof 322 nm;

FIG. 9 is a graph showing the ratio between transmittance of theUV-region (200 nm or more but 400 nm or less) and transmittance ofwavelength (longer than 400 nm but 1000 nm or less) excluding theUV-region in the whole transmittance;

FIGS. 10A and 10B are views showing the exterior and sectional structureof first and second embodiments (applied examples of the UV-bandpassfilter according to the present invention) in the UV-detecting apparatusaccording to the present invention, respectively;

FIG. 11 is a graph showing wavelength dependence characteristics oflight-receiving sensitivity in UV-detecting apparatus according to thesecond embodiment shown in FIG. 10B and in a conventional photodetectorwhich is a comparative example;

FIG. 12 is a view showing a sectional structure of a third embodiment inthe UV-detecting apparatus according to the present invention;

FIG. 13 is a view showing the exterior of a first embodiment (appliedexample of the UV-bandpass filter according to the present invention) inthe light-emitting apparatus according to the present invention; and

FIGS. 14A and 14B are views showing schematic configurations of secondand third embodiments in the light-emitting apparatus according to thepresent invention, respectively.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, embodiments of the UV-bandpass filter, UV-detectingapparatus, and light-emitting apparatus according to the presentinvention will be explained in detail with reference to FIGS. 2A to 2C,3 to 9, 10A, 10B, 11 to 13, 14A, and 14B. In the explanation of thedrawings, identical members and parts will be referred to with identicalnumbers without repeating their overlapping descriptions.

UV-bandpass Filter

FIGS. 2A to 2C are views showing respective structures of first to thirdembodiments of the UV-bandpass filter according to the presentinvention. The UV-bandpass filter 1 according to the first embodimentshown in FIG. 2A comprises a UV-transmitting member 20, such as acrylicresin or silica glass, transparent to UV-rays and a thin silver film 10having a thickness T (formable upon vapor deposition, for example)formed on a surface of the UV-transmitting member 20. The thin silverfilm 10 comprises an entrance face 10 a and an exit face 10 b foremitting light in a specific UV-region having a wavelength ranging from200 nm to 400 nm, preferably a wavelength ranging from 250 nm to 400 nm,more preferably a wavelength ranging from 300 nm to 360 nm, in the lighthaving reached the entrance face 10 a. In the UV-bandpass filter 1according to the present invention, the thin silver film 10 has athickness T of 70 nm or more, preferably 80 nm or less, so as tosuppress the transmittance with respect to light having wavelengthsexcluding the specific UV-region to 10% or less, preferably 5% or less.On the other hand, it is necessary for the thickness T of the thinsilver film 10 to be set to 250 nm or less in order to secure atransmittance of 5% ormore with respect to light having awavelengthincluded in the specific UV-region.

The UV-bandpass filter 2 according to the second embodiment shown inFIG. 2B comprises a thin silver film 11 having a thickness T, whilehaving a laminate structure in which a UV-transmitting member 21 a and aUV-transmitting member 21 b are in contact with the entrance face 11 aand exit face 11 b of the thin silver film 11, respectively. TheUV-bandpass filter 2 according to the second embodiment is obtained whena surface of one of the UV-transmitting members 21 a, 21 b is formedwith the thin silver film 11 and then the UV-transmitting members 21 a,21 b are arranged so as to sandwitch thus formed thin silver film 11.

The thin silver film 10 has a thickness T of 70 nm or more, preferably80 nm or more, so as to suppress the transmittance with respect to lighthaving wavelengths excluding the specific UV-region to 10% or less,preferably 5% or less, in the UV-bandpass filter 2 according to thesecond embodiment as well. On the other hand, it is necessary for thethickness T of the thin silver film 10 to be set to 250 nm or less inorder to secure a transmittance of 5% or more with respect to lighthaving a wavelength included in the specific UV-region.

The UV-bandpass filter 3 according to the third embodiment shown in FIG.2C comprises a UV-transmitting member 22 and thin silver films 12, 13,each having a thickness T/2, formed on opposite main faces of theUV-transmitting member 22. The thin silver film 12 comprises an entranceface 12 a and an exit face 12 b for emitting light in the UV-region inthe light having reached the entrance face 12 a. On the other hand, thethin silver film 13 comprises an entrance face 13 a and an exit face 13b for emitting light in the UV-region in the light having reached theentrance face 13 a. It is not always necessary for the thin silver films12, 13 to have the same thickness as long as their total thickness is T.Also, the number of thin silver films is not limited to 2 (the laminatestructure may have two or more thin silver films having a totalthickness of T).

The total thickness (T) of the thin silver films 12, 13 is designed soas to become 70 nm or more, preferably 80 nm or more, in order tosuppress the transmittance with respect to light having wavelengthsexcluding the specific UV-region to 10% or less, preferably 5% or less.On the other hand, it is necessary for the total thickness T to be setto 250 nm or less in order to secure a transmittance of 5% or more withrespect to light having a wavelength included in the specific UV-region.

The inventors prepared 11 kinds of samples having respective thicknesses(12.8 nm to 400.0 nm) different from each other, and measuredtransmission characteristics of these samples. Each of thus preparedsamples comprised a structure similar to that of the UV-bandpass filter1 according to the first embodiment shown in FIG. 2A, and was made byforming a thin silver film with a predetermined thickness on a surfaceof silica glass. FIG. 3 is a graph showing wavelength dependencecharacteristics concerning five kinds of thin silver films havingthicknesses of 12.8 nm, 28.8 nm, 46.4 nm, 59.2 nm, and 78.4 nm,respectively; whereas FIG. 5 is a graph showing wavelength dependencecharacteristics concerning six kinds of thin silver films havingthicknesses of 80.4 nm, 106.4 nm, 135.2 nm, 160.8 nm, 241.2 nm, and400.0 nm, respectively.

In FIG. 3, curves G210, G220, G230, G240, and G250 show wavelengthdependence characteristics of transmittance concerning thin silver filmshaving thicknesses of 12.8 nm, 28.8 nm, 46.4 nm, 59.2 nm, and 78.4 nm,respectively. FIG. 4 is a graph showing respective wavelength dependencecharacteristics of relative transmittance in the five kinds of thinsilver films shown in FIG. 3 when their maximum transmittances are takenas 100%, in which curves G310, G320, G330, G340, and G350 correspond tocurves G210, G220, G230, G240, and G250 in FIG. 3, respectively.

In FIG. 5, curves G410, G420, G430, G440, G450, and G460 show wavelengthdependence characteristics of transmittance concerning thin silver filmshaving thicknesses of 80.4 nm, 106.4 nm, 135.2 nm, 160.8 nm, 241.2 nm,and 400.0 nm, respectively. FIG. 6 is a graph showing respectivewavelength dependence characteristics of relative transmittance in thesix kinds of thin silver films shown in FIG. 5 when their maximumtransmittances are taken as 100%, in which curves G510, G520, G530,G540, G550, and G560 correspond to curves G410, G420, G430, G440, G450,and G460 in FIG. 5, respectively.

As can be seen from the curves shown in FIGS. 3 to 6, each of the 11kinds of prepared samples has a transmission characteristic in whichonly one peak exists at a wavelength of 322 nm in the wavelength band of200 nm to 1000 nm. According to the measurement conducted by theinventors, only one transmission peak exists even in the wavelength bandof 200 nm to 3000 nm. When a thin silver film is employed in aUV-bandpass filter, it is necessary for the thin silver film to have asufficient transmission characteristic with respect to light having awavelength included in the UV-region (UV-rays) while having a sufficientblocking characteristic with respect to light having wavelengthsexcluding the UV-region.

Therefore, the inventors studied the relationship between film thickness(Ag film thickness) and transmittance concerning light having awavelength of 322 nm which is the transmission peak wavelength of thethin silver film. In FIG. 7, curve G610 shows the relationship betweenthickness and transmittance of a thin silver film with respect to lighthaving a wavelength of 322 nm (transmission peak wavelength) As can beseen from this curve G610, while the maximum transmission amount of thethin silver film decreases as the film thickness increases, atransmittance of at least 5% is required to be secured in order to makeit possible for the light transmitted through the thin silver film(UV-rays) to be received by photodetectors. From this fact, it is seenthat the maximum thickness of a thin silver film suitable for aUV-bandpass filter is preferably 250 nm or less.

On the other hand, FIG. 8 is a graph showing respective relationshipsbetween thickness and relative transmittance with respect to a pluralityof wavelengths (400 nm, 500 nm, and 600 nm) of light. In FIG. 8, therelative transmittance is a transmittance with reference to the maximumtransmittance (taken as 100%) at a transmission peak wavelength of 322nm. In FIG. 8, curves G710, G720, and G730 show relationships betweenthickness and relative transmittance with respect to light havingwavelengths of 400 nm, 500 nm, and 600 nm, respectively. In order for athin silver film to function as a UV-bandpass filter, it is necessaryfor at least the transmittance with respect to light having a wavelengthof 400 nm or longer to be suppressed to 10% or less, preferably 5% orless. As a consequence, it is seen that the minimum thickness of a thinsilver film suitable for a UV-bandpass filter is required to be 70 nm ormore, preferably 80 nm or more.

FIG. 9 is a graph showing the ratio between transmittance of theUV-region (200 nm or more but 400 nm or less) and transmittance ofwavelength (longer than 400 nm but 1000 nm or less) excluding theUV-region in the whole transmittance (measured in the wavelength rangeof 200 nm to 1000 nm) concerning a plurality of samples having filmthicknesses (Ag film thicknesses) different from each other. In thegraph shown in FIG. 9, region P1 indicates the ratio of transmittance inthe UV-region, whereas region P2 shows the ratio of transmission ofwavelengths excluding the UV-region. As can be seen from this graph, theratio of wavelengths excluding the UV-region in the whole transmittancecan be reduced to 10% or less if the film thickness is 70 nm or more,preferably 80 nm or more (the ratio of transmittance of wavelengthsexcluding the UV-region in the whole transmittance decreases to 1/10000or less if the film thickness is about 240 nm).

UV-detecting Apparatus

As in the foregoing, the UV-bandpass filter according to the presentinvention is constituted by a single silver layer regulated so as tohave a predetermined thickness, whereby it can be combined with variouskinds of optical devices such as light-receiving devices andlight-emitting device. In the following explanation, a UV-detectingapparatus employing the UV-bandpass filter according to the presentinvention will mainly be explained. FIGS. 10A and 10B are views showingthe exterior and sectional structure of first and second embodiments inthe UV-detecting apparatus according to the present invention,respectively.

The UV-detecting apparatus 300 according to the first embodimentcomprises the simplest structure as shown in FIG. 10A, and isconstituted by a UV-bandpass filter 1 such as the one shown in FIG. 2A,and a commercially available photodiode 30 (of can type). Though theUV-detecting apparatus 300 according to the first embodiment employs theUV-bandpass filter 1 having a thin silver film 10 formed on aUV-transmitting member 20 acting as a reinforcement plate, the thinsilver film 10 may be formed on a surface 30 a facing the photodiode 30as well.

FIG. 10B is a view showing the sectional structure of the UV-detectingapparatus 40 according to the second embodiment, in which theUV-bandpass filter 1 shown in FIG. 2A is employed as an entrancefaceplate. The UV-detecting apparatus 40 according to the secondembodiment comprises a ceramic case 41, leadpins 42 penetrating throughthe bottom part of the case 41, a photodiode 43 bonded to the bottompart of the case 41 with the aid of a die-bonding material 44, and anentrance faceplate (corresponding to the UV-bandpass filter 1) securedto the opening part of the case 41 by a silicone resin adhesive 45.Though the material of the case 41 is ceramic in the UV-detectingapparatus 40 according to the second embodiment, it may be a resin ormetal as well. The photodiode 43 installed within the case 41 may be asemiconductor device such as phototransistor or avalanche photodiode, ora light-receiving IC or CCD accompanying circuits. The adhesive 45 forbonding the case 41 and the entrance faceplate, which is a UV-bandpassfilter, to each other is not limited to silicone resins, but may beinorganic soldering materials or glass materials, for example, as longas they are adhesives which do not affect the transmission of UV-rays.The thin silver film constituting a part of the entrance faceplate maybe formed on the surface opposing the photodiode 43 within the case 41as well.

FIG. 11 is a graph showing respective wavelength dependencecharacteristics of light-receiving sensitivity in the UV-detectingapparatus 40 having the structure shown in FIG. 10B and in aconventional photodetector (including no thin silver film as aUV-bandpass filter) . In the samples prepared as the UV-detectingapparatus, thin silver films formed on the surface of silica glass 20have thicknesses of 46.4 nm, 78.4 nm, and 106.4 nm, respectively. On theother hand, the photodiode prepared as the comparative example is asilicon photodiode.

In FIG. 11, curves G810, G820, G830, and G840 show respective wavelengthdependence characteristics of light-receiving sensitivity in the siliconphotodiode and in the samples formed with thin silver films havingthicknesses of 46.4 nm, 78.4 nm, and 106.4 nm, respectively.

As can be seen from the graph of FIG. 11, the photodetector (siliconphotodiode), which is a comparative example, has a high light-receivingcharacteristic in the vicinity of 1000 nm (see curve G810), whereas eachof the samples having a thin silver film formed on the entrancefaceplate has only one transmission peak at a wavelength of 322 nm,thereby being able to effectively block light near a wavelength of 1000nm (see curves G820, G830, and G840). In particular, among the samplesformed with thin silver films, those formed with thin respective silverfilms having thicknesses of 78.4 nm and 106.4 nm exhibit sufficientblocking characteristics with respect to light having wavelengthsexcluding the UV-region (see curves G830 and G840).

Though the above-mentioned UV-detecting apparatus according to thesecond embodiment employs a UV-bandpass filter 1 having a thin silverfilm formed on the surface of silica glass 20 (see FIG. 2A) as anentrance faceplate, the thin silver film may directly be formed on thelight-receiving face of a photodiode. FIG. 12 is a view showing thesectional structure of a third embodiment in the UV-detecting apparatusaccording to the present invention.

The UV-detecting apparatus 50 (photodiode) according to the thirdembodiment comprises a monocrystal N-type silicon substrate 51. Thesubstrate 51 is formed with a P⁺ region in which impurities such asboron are injected, and an N⁺ region in which impurities such asphosphorus are injected, whereas the front face of the substrate 51 isformed with an insulating film (SiO₂ or Si₃N₄) 52 for protecting thesurface of the substrate 51 and A1 electrodes 53. A thin silver film100, acting as the UV-bandpass filter according to the presentinvention, is directly formed on the light-receiving region of thephotodiode comprising the foregoing configuration. When the UV-bandpassfilter is employed in a light-receiving device made of an inexpensivesilicon material as such, a UV-detecting apparatus can be obtained at alower cost.

The insulating film 52 on the light-receiving region has a thicknessregulated so as to yield a low reflectivity with respect to UV-rays,thereby improving the light-receiving sensitivity. In place ofsignal-taking electrodes from the N⁺ region of the substrate 51, an N⁺layer and an Au layer may successively be formed on the rear face of thesubstrate 51, so that the Au layer is employed as a signal-takingelectrode. Though the substrate 51 is of N type, it may be of P type aswell. The substrate material is not limited to silicon, but may be acompound semiconductor such as GaAsP, for example. Though theUV-detecting apparatus according to the third embodiment is a photodiodein which a thin silver film is formed as a UV-bandpass filter, it mayalso have a configuration in which a thin silver film is directly formedin the light-receiving region of a light-receiving IC or CCDaccompanying circuits, or a semiconductor device such as phototransistoror avalanche photodiode.

UV Source

A UV source employing the UV-bandpass filter according to the presentinvention will now be explained. FIG. 13 is a view showing the exteriorof a first embodiment in the UV source (light-emitting apparatus)according to the present invention.

The UV source 60 according to the first embodiment comprises astructure, for example, in which a thin silver film 610, which is aUV-bandpass filter according to the present invention, is directlyformed on the surface of a glass envelope 600 of a xenon lamp emittinglight upon discharging therewithin. The light-emitting apparatusaccording to the present invention is not limited to the xenon lamp asin the first embodiment, whereas UV sources can also be obtained inlamps of mercury-xenon, halogen, metal halide, and the like, forexample.

FIGS. 14A and 14B are views showing respective schematic structures ofsecond and third embodiments in the UV source (light-emitting apparatus)according to the present invention.

As shown in FIG. 14A, the UV source 70 according to the secondembodiment comprises a lamp light source 72 of xenon, mercury-xenon,halogen, metal halide, and the like, a container 71 for accommodatingthe lamp light source 72, and a light valve 73 such as an optical fiberhaving a front end part secured to the container 71, whereas aUV-bandpass filter 74 is disposed between the light entrance end of thelight valve 73 and the lamp light source 72. Though the UV source 70according to the second embodiment shows the UV-bandpass filter 74comprising a structure similar to that of the UV-bandpass filter 1 shownin FIG. 2A, it may be a UV-bandpass filter having a structure such asone shown in FIG. 2B or 2C as well. Also, it may have a structure inwhich a thin silver film is directly formed at the light entrance end ofthe light valve 73.

As shown in FIG. 14B, the UV source 80 according to the third embodimentcomprises a lamp light source 82 of xenon, mercury-xenon, halogen, metalhalide, and the like, a container 81 for accommodating the lamp lightsource 82, and a light valve 83 such as an optical fiber having a frontend part secured to the container 81, whereas a UV-bandpass filter 84 isdisposed at the light exit end of the light valve 83. Though the UVsource 80 according to the third embodiment also shows the UV-bandpassfilter 84 comprising a structure similar to the UV-bandpass filter 1shown in FIG. 2A, it may be a UV-bandpass filter having a structure suchas one shown in FIG. 2B or 2C as well. Also, it may have a structure inwhich a thin silver film is directly formed at the light entrance end ofthe light valve 83.

Though a single silver film is employed as the thin silver film 10,which is a UV-bandpass filter, in each embodiment in the UV-bandpassfilter, UV apparatus, and light-emitting apparatus according to thepresent invention, the thin silver film 10 also includes a film formedlike an island having a gap of not greater than a wavelength oftransmitted light.

From the foregoing explanations of the invention, it will be obviousthat the same may be varied in many ways. Such variations are not to beregarded as a departure from the spirit and scope of the invention, andall such modifications as would be obvious to one skilled in the art areintended to be included within the scope of the following claims.

INDUSTRIAL APPLICABILITY

According to the present invention, a single silver film regulated so asto have a predetermined thickness constitutes a bandpass filter having asufficient blocking effect with respect to light having wavelengthsexcluding the UV-region, which is applicable to a wider range oftechnology when combined with conventional optical devices, and canfunction as a UV-bandpass filter in a wider wavelength band when thefilm thickness of the thin silver film is regulated to 70 nm or more,preferably 80 nm or more, but 250 nm or less.

1. A UV-bandpass filter for selectively transmitting light having awavelength included in a specific UV region of 200 nm to 400 nm,comprising: a UV-transmitting member that is transparent to at least thelight included in said specific UV region; and a thin silver film havingan entrance face and an exit face that opposes said entrance face andthat is in direct contact with one surface of said UV-transmittingmember, said thin silver film having such a total thickness of at least80 nm but not greater than 250 nm, as to make the ratio of power oflight transmitted from said exit face to power of light incident uponsaid entrance face be not greater than 10% at any wavelength in awavelength region of 400 nm to 3000 nm.
 2. The UV-bandpass filteraccording to claim 1, wherein the ratio of the total power of the lightexcluding said specific UV-region, which is included in the lighttransmitted from said exit face, to the total power of the lighttransmitted from said exit face is not greater than 10%.
 3. AUV-detecting apparatus including the UV-bandpass filter according toclaim
 1. 4. A light-emitting apparatus including the UV-bandpass filteraccording to claim
 1. 5. The UV bandpass filter according to claim 1,wherein said thin silver film includes a plurality of silver layersconstituting a laminate structure.